Prime Distance—-篩素數

題目：http://poj.org/problem?id=2689

原始碼：

#include <stdio.h>__int64 l,u;int prime[47000];int prime1[1000100];int is[47000],is1[1000100];int cou=0,cou1;int min,max;int a,b;void getPrime(){    for(int i=2;i<46400;i++) is[i]=1;    for(int i=2;i<46400;i++)        {            if(is[i])  prime[cou++]=i;            for(int j=0;j<cou&&i*prime[j]<46400;j++)            {                is[i*prime[j]]=0;                if(i%prime[j]==0)  break;            }       }}void solve(__int64 l,__int64 u){    __int64 p,s;    if(u<46400)    {      for(int i=l;i<=u;i++)       if(is[i])       prime1[cou1++]=i-l;    }    else    {      for(int i=0;i<=u-l;i++)   is1[i]=1;      for(int i=0;i<cou&&prime[i]*prime[i]<=u;i++)         {             s=l/prime[i];             if(s*prime[i]<l)  s++;             if(s<=1) s++;             for(__int64 j=s;j*prime[i]<=u;j++)              {                //   printf("%I64d\n",j*prime[i]);                  p=(int)j*prime[i]-l;                  is1[p]=0;              }         }      for(int i=0;i<=u-l;i++)       if(is1[i])       prime1[cou1++]=i;    }}int main(){ //   freopen("D:\\in.txt","r",stdin);    getPrime();    while(scanf("%lld %lld",&l,&u)!=EOF)    {       cou1=0;       solve(l,u);       min=2147483647;       max=-1;       if(cou1<2)       {           printf("There are no adjacent primes.\n");           continue;       }       for(int i=0;i<cou1-1;i++)       {           if(prime1[i+1]-prime1[i]<min)           {               min=prime1[i+1]-prime1[i];               a=i;           }           if(prime1[i+1]-prime1[i]>max)           {               max=prime1[i+1]-prime1[i];               b=i;           }       }       printf("%I64d,%I64d are closest, %I64d,%I64d are most distant.\n",prime1[a]+l,prime1[a+1]+l,prime1[b]+l,prime1[b+1]+l);    }}